As is known, operating electronic devices produce heat. This heat should be removed from the devices in order to maintain device junction temperatures within desirable limits: failure to remove the heat thus produced results in increased device temperatures, potentially leading to thermal runaway conditions. Several trends in the electronics industry have combined to increase the importance of thermal management, including heat removal for electronic devices, including technologies where thermal management has traditionally been less of a concern, such as CMOS. In particular, the need for faster and more densely packed circuits has had a direct impact on the importance of thermal management. First, power dissipation, and therefore heat production, increases as the device operating frequencies increase. Second, increased operating frequencies may be possible at lower device junction temperatures. Finally, as more and more devices are packed onto a single chip, power density (Watts/cm2) increases, resulting in the need to remove more power from a given size chip or module. These trends have combined to create applications where it is no longer desirable to remove the heat from modern devices solely by traditional air cooling methods, such as by using traditional air cooled heat sinks.
While alternatives to air cooling are known, such as chilled water and refrigeration systems, these alternatives tend to increase both manufacturing and operational costs, and therefore tend to be applied primarily in high performance applications. Methods are therefore desirable which augment traditional air cooling methods, thereby overcoming at least some of the limitations of traditional methods, without introducing costly refrigeration or chilled water distribution systems.
In general, enhanced air cooling may be achieved by modifying any of a number of parameters, such as ambient air temperature, airflow rate, heatsink surface area, etc. While an increase in any of these factors tends to improve the efficiency with which heat transfers from heatsink fins to ambient air, design considerations may place practical limitations on the extent to which any parameter may be increased, and interactions between the various parameters may limit the effectiveness of a particular parameter change. For example, ambient air temperatures are typically controlled by customer environmental systems, within established limits. Electronic systems are designed to operate within existing customer installations, and typically do not have the flexibility to require reduced ambient air temperatures. Furthermore, many electronic applications are constrained to occupy a limited volume or footprint (i.e. floor surface area). Increases in fin surface area, therefore, are likely accomplished by decreasing fin thickness and increasing fin density, effectively increasing fin surface area within a constant heatsink volume. As fin density thus increases, however, so does the pressure differential between airflow entering the fins and airflow leaving the fins. Both airflow rates and pressure drops are frequently limited by other design considerations, such as acoustic constraints.
Many modern electronic systems are designed in a rack configuration, such as prior art rack 110 illustrated in FIGS. 1A and 1B. Typical electronic rack systems such as rack 110 include several electronics drawers 120, also illustrated in FIG. 2. Each drawer 120 may include an entire electronics subsystem. Air cooling of electronics within drawers 120 is accomplished by using an air moving device mounted within each drawer, such as fan 129, to create an airflow within the drawer. As illustrated in FIGS. 1A, 1B, and 2, fan 129 causes ambient air to enter each drawer 120 through air inlet 127a in drawer front 126, flow over devices 138 and heatsink 136 within each drawer, and exit the rear of each drawer through air outlet 127b in drawer back 128.
Volume constraints are particularly critical in modern electronic rack systems such as rack 110, having several drawers 120 each containing electronic subsystems. Each drawer 120 is constrained to fit within a relatively small volume. High power components within these drawers, such as processor module 132, typically have a limited volume of space immediately adjacent to the component within which to place a heatsink, such as heatsink 136. The drawer volume constraints therefore place a design limitation on the maximum size heatsink that can be directly attached to a high power device. This places a practical limitation on the extent to which high power devices such as processor 132 may be air cooled within a limited volume drawer.
Electronics drawers typically utilize only a portion of the volume within the drawer, as illustrated in FIG. 2. The available volume may not be conveniently located adjacent to a high power device, however, such as processor 132, and therefore may not provide a volume into which a traditional heat sink directly attached to a high power device may be extended.
For the foregoing reasons, therefore, there is a need in the art for an apparatus capable of utilizing the available unused volume within an electronics drawer to provide enhanced air cooling of high power electronic components within the drawer.